1. Field of the Invention
This invention relates to a framework assembly for enclosing an array of heat exchanger tubes and providing protection during shipping and/or providing support of the tubes during a vertical tubing operation. More particularly, the invention relates to the particular framework adjacent and engaging the U-bend portion of the heat exchanger tubes which, during the final loading of the tubes into the heat exchanger, supports the heat exchanger tubes and provides a clamping force preventing relative movement of the tubes while permitting the individual release of each tube within the array of tubes supported by the framework.
2. Description of the Prior Art
This invention is an improvement of the apparatus described in copending U.S. patent application Ser. No. 965,017, filed Nov. 30, 1978, now U.S. Pat. No. 4,202,085, and having a common assignee of the present invention.
In the apparatus of the above-identified application, a U-tube support framework is shown in which a double column of U-shaped heat exchanger tubes are disposed in proper arrangement for subsequent vertical insertion into the tubesheet of a heat exchanger such as a steam generator. The tubes are disposed and retained therein in the relative positions in which the tubes will be finally installed in the tubesheet. Such framework generally comprises an upper rack portion corresponding to the U-bend portion of the tubes and having structure for lifting the tubes to a vertical position, and a rectangular lower portion for protecting the tubes during shipping and aligning the long straight-leg portions of the tubes prior to installation. Further, proper disposition of the legs within the lower portion is assurance that the tubes are properly formed and aligned for insertion into aligned apertures in the support plates and tubesheet of the heat exchanger.
The sequence for vertically inserting the tubes generally comprises sequentially removing serially connected sub-assemblies of the lower portion of the assembly as the U-tubes are lowered from an elevated aligned position above the tube support plates of the heat exchanger by a hoist attached to the rack portion of the framework. Guides in the lower ends of the tubes guide the tubes through aligned apertures in the tube support plates and finally into the tubesheet. However, it has been found that regardless of the care taken in properly aligning the tubes, there remains the probability that at least one end of one tube in the array, which in this instance is a double column of U-tubes enclosed by the framework assembly, will be prevented from fully entering the tubesheet because of frictional engagement between the tube and any or all of the openings through which it passes. Further, because great care must be exercised to prevent any scratching of the tubes that may lead to a premature failure, once any one end of a tube is frictionally prevented from further movement under its own weight, additional force, up to some preselected maximum force which corresponds to the tube being inserted without concern for scratching, must be applied to complete the proper positioning of the tube within the heat exchanger.
As the upper rack portion of the above-identified patent application supported the U-bend portion of the tubes without clamping them, the tubes were generally free to move with respect to one another and if any end of a tube became frictionally engaged to the extent that during further lowering of the support rack such end did not move downwardly, the tube would be displaced axially in the rack (i.e. with both ends of the tube initially being flush, preventing one end from moving while the remainder of the tube was being lowered would cause the opposite end to move downwardly an exaggerated amount and was referred to as "snaking"). Thus, in such a rack portion of the prior art, if a tube became frictionally engaged, further lowering of the tube bundle caused increasing misalignment of the tube ends. To alleviate this problem, it was necessary to remove from the rack the tube which became stuck, and insert it manually. However, because of the construction of the above-referenced rack, it was necessary to free all the tubes supported by the rack. In such instances, the U-bends of the tubes would become unrestrained and free to move about, causing them to become entangled and further complicating the tubing procedure.